Switching devices are utilized widely in industrial and commercial applications. Switches come in a variety of shapes and sizes. Some are large and cumbersome, while others are produced at the micro mechanical level. A particular need exists for mechanically actuated switches that are small in size, highly reliable, exhibit high accuracy, and can operate in harsh environments. This type of switch is typically required for use in commercial and military aviation applications. For example, such switches must be able to operate in particularly cold environments such as the Arctic or at extremely high altitudes, while other switches must be able to operate under difficult pressures, such as that experienced by submarines.
The operation of switches that are utilized for such applications is typically based on a set of metallic contacts that are actuated to accomplish the switching action. The moving parts associated with such switch contacts can wear and cause unreliable switch operation. The moving parts of such switches also provide a leak path that must generally be sealed to prevent contamination of the switch contacts. An additional problem experienced with conventional switches is that the contacts can become oxidized during normal use and fail to switch at low currents and at low voltage loads.
The present inventors have concluded, based on the foregoing, that the need for an improved mechanically actuated switch can be solved through the use of a unique switch arrangement, which is described in greater detail herein. In particular, the present inventors believe that the use of magnetoresistive-based devices can improve the operating life and efficiency of a mechanically actuated switch.
Magnetoresistive devices are well known in the art. A magnetoresistor (MR) is typically configured as a two terminal device that changes its resistance in accordance with a variation in a magnetic field. Almost every conducting material exhibits some magnetoresistance. The magnetoresistive effect, however, is particularly large in permalloys, which include nickel-iron alloys, and other ferromagnetic materials. Because magnetoresistive-based devices are very sensitive to magnetic fields, the present inventors believe such devices will find useful applications in switches.
An example of a magnetoresistive-based device is a magnetoresistive sensor. Magnetoresistive sensors are utilized in many solid-state applications. These include, for example, automotive, marine, military, industrial, aircraft and space applications. Signature detection systems make use of magnetoresistive sensors for traffic and vehicle control, mine detection and weapons systems, and metal detection such as mining, separation and security. In addition, magnetoresistive sensors have been utilized for anomaly detection such as proximity detection and position detection, whether angular or linear. To date, however, magnetoresistive devices have not been utilized successfully to implement mechanically actuated switching devices.
An example of a magnetoresistive sensor is disclosed in U.S. Pat. No. 5,500,590, “Apparatus for Sensing Magnetic Fields Using a Coupled Film Magnetoresistive Transducer” to Bharat B. Pant, which issued on Mar. 19, 1996, and is assigned to Honeywell Inc. (“Honeywell”) of Minneapolis, Minn. U.S. Pat. No. 5,500,590 generally describes a first magnetically coupled film sensing element and a second magnetically coupled film sensing element that are arranged to change resistance in response to a magnetic field when biased by a current through the elements. A current carrying conductor spaced from the elements sets the magnetization in the elements. A transfer function of the elements is adjusted by varying the current through the elements or the current through the conductor.
Another example of a magnetoresistive sensor is disclosed in U.S. Pat. No. 5,497,082, “Quadrature Detector with a Hall Effect Element and a Magnetoresistive Element,” which issued to Peter G. Hancock on Mar. 5, 1996, and is also assigned to Honeywell. U.S. Pat. No. 5,497,082 describes a position sensor with the capability of detecting a quadrature signal by the provision of first and second magnetically sensitive devices. The first magnetically sensitive device comprises a Hall effect element or some other device, which is capable of sensing strength of a component of a magnetic field, and which is perpendicular to a pre-selected plane. A second magnetically sensitive device is provided that is capable of sensing the component of a magnetic field lying in the same plane.
Thus, the present inventors have concluded that the use of a magnetoresistive device in association with a mechanically actuated switch can result in improved switching action, while avoiding the aforementioned problems, such as oxidation of the contacts and undesirable part wear.